1. Field of the Invention
The present invention relates to a biometric apparatus for measuring biometric data and, more specifically to a biometric apparatus which carries out zero-point reset when the biometric apparatus is not in use.
2. Description of the Related Art
In the related art, various types of biometric apparatuses for measuring biometric data such as the weight, the percent body fat, the amount of body fat of a measured person are used and, a body-fat-meter-integrated weighing machine is widely used for example, at home, as one of the biometric apparatuses. Such body-fat-meter-integrated weighting machine generally includes an electrode member for measuring bioimpedance (electric resistance) of a measured person disposed on an upper surface of a body, and a weight measuring unit at a position corresponding to the electrode member. The weight measuring unit includes a load cell composed of a distortable member formed of a metallic member which is deformed according to an applied load and a strain gauge (sensor) attached to the distortable member, and the strain gauge expands or contracts according to the deformation of the distortable member due to the application of load, so that the weight of the measured person is calculated by a change of the value of resistance (output value) according to the expansion and contraction of the strain gauge as a change of a load signal output. To use such the body-fat-meter-integrated weighting machine, after having turned the power on, the measured person rides on the body, so that the biometric data such as the weight or the percent body fat is measured.
When the measured person uses the body-fat-meter-integrated weighting machine, it is necessary to place the body-fat-meter-integrated weighting machine on the floor in the room horizontally, and set the output value of the load cell in an unloaded state before the measured person rides on the body to zero point, so-called zero-point reset. It is because the weight of the measured person is measured on the basis of the difference between an output value of the load cell when the measured person rides on the weighting machine and an output value of the load cell in an unloaded state. The biometric data such as the percent body fat or the amount of body fat is obtained also by the bioimpedance measured by flowing weak constant current from the electrode members to the bottom of the measured person's feet. However, since the biometric data is computed on the basis of consideration of the weight of the measured person, adequate zero-point reset is important for obtaining accurate biometric data (JP-A-62-126318).
The body-fat-meter-integrated weighting machine in the related art as described above is generally set to put the power on first, then, after having waited until the output of the load cell is stabilized, carry out the zero-point reset. Therefore it is not convenient for the measured person because he/she cannot ride on the platform and start measurement quickly when he/she wants to measure the biometric data. Therefore there is proposed a so-called step-on type biometric apparatus which completes the zero-point reset at predetermined intervals, starts up when it detects that the measured person rides on the biometric apparatus, so that the measurement of the biometric data may be started quickly when the measured person does not use the biometric apparatus.
However, even in the case of the step-on type biometric apparatus as described above, the state of installation of the biometric apparatus when it is not in use is not necessarily in a state suitable for the zero-point setting. For example, when the biometric apparatus is stored, it may be stored in a state of being propped against a wall with one side down, or may be stored in a state in which one side of the body is in touch with the wall, which are not necessarily suitable for the zero-point reset. Therefore, when the zero-point reset of the output value of the load cell in such states which is not suitable for the zero-point reset of the biometric apparatus, the biometric data such as the weight may be calculated on the basis of the incorrect zero-point, and hence there may arise a problem in which an accurate biometric data are not measured.
Even when the biometric apparatus is installed horizontally, when an output value of the load cell is to be detected for the zero-point reset, there is a case in which the value is fluctuated due to the influence of, for example, vibrations generated around the biometric apparatus. Therefore, in order to achieve the zero-point reset accurately, it is necessary to detect the output value of the load cell for a certain period of time and reset the zero point when the output value is stabilized.